Inert foreign bodies ingested from polluted air or implanted surgically are carcinogenic in man and in experimental animals. The induction of tumors by these agents is mechanistically puzzling and not obviously reconcilable with a mutagenic mode of action. Macrophages and circulating blood platelets secret "wound hormones" which are potent mitogens for normal fibroblasts in tissue culture. The objective of this research is to explore the role of platelet and macrophage derived wound hormones as modulators of connective tissue growth in animals and as mediators of the neoplastic response to inert foreign bodies. Towards this objective the technologies of biochemistry and cell culture will be mutually brought to bear. The congenitally athymic "nude mouse" will be used as a reliable and physiologically meaningful means of detecting malignantly transformed cells. Synthetic cell culture medium will be prepared using plasma rather than serum as a media supplement. The capacity of human and animal fibroblasts to proliferate in plasma-supplemented culture medium will be related to tumorigenic potential in nude mice. The capacity of inert foreign bodies to generate local concentrations of "wound hormones" in vivo will be related to the carcinogenic action of these materials.